1. Field of the Invention
This invention relates to a track follow-up control apparatus for an optical disc device having a plurality of heads carried on a common slider.
2. Related Background Art
In a track follow-up control apparatus for an optical disc device, a head provided with a tracking actuator capable of scanning a light beam on the surface of an optical disc radially thereof by the driving of a galvano mirror or the like is carried on a slider movable in the radial direction of the optical disc, and position control of the slider and the control of the tracking actuator of the head are effected simultaneously, whereby two-step servo tracking control in which the light beam is caused to follow a desired track is accomplished.
Taking as an example a slider control employing a sense signal which detects the inclination of a beam, the position of the slider is controlled on the basis of the sense signal after the access of a desired track while, on the other hand, for any variation in the track position which cannot be followed by the slider position control, track following is controlled on the basis of a tracking error signal (a signal which detects how much the light beam deviates from the desired track) by driving a galvano mirror by a tracking actuator provided on a head, whereby the light beam is caused to precisely follow the desired track.
Also, in a slider control employing a tracking error signal, a light beam is caused to follow a track by the slider position control for a lengthy variation in the track position which is attributable to the eccentricity of the optical disc, in addition to the predetermined position control of the slider based on a sense signal, while for a brief variation in the track position, an amount which cannot be followed in the slider position control is made up for by the driving of the galvano mirror by the tracking actuator provided on the head, whereby the light beam is caused to precisely follow a track.